This invention relates to a method of making particles of hydrous trivalent chromium oxide intimately associated with a carbonaceous substrate, to the particles themselves, and to a method of using the particles to produce metallic chromium.
Chromium is one of a number of metals that are used to form alloys for use in the aerospace and other industries. For example, nickel, cobalt, chromium, and molybdenum are used to form "superalloy" which is used in the aerospace industry. Very high purity metals are required to form these alloys because the slightest amount of impurity can seriously detract from the properties of the resulting alloy. For many of these alloys, chromium is the dirtiest metal that is used in forming them.
High purity chromium can be produced electrolytically, but that process is very capital intensive and is quite expensive. In another method of making metallic chromium, finely divided chromic oxide, Cr.sub.2 O.sub.3, is physically mixed with finely divided carbon and a binder. The mixture is briquetted to aid the diffusion controlled reaction and the resulting briquettes are roasted under a reduced pressure, so that the carbon reduces the chromic oxide to metallic chromium. Because it is difficult to insure a homogenous mixture of carbon and Cr.sub.2 O.sub.3 in the briquettes, the production of a suitably pure metal typically involves reprocessing the partially reacted briquettes by grinding, adjusting the stoichiometry of the reactants (if necessary), re-briquetting, and re-roasting. While this process can produce the high purity chromium required for many alloys, it is also a very expensive process.